Method of drying vulcanized fiber sheets



Dec. 26, 1 939. N. G. JoNEs METHOD OF DRYING VULCANIZED FIBER SHEETS Filed J une .J... ...........4....:..,. A l h IA f lll. l .I I/ A l l l Il l/.v I.- l IUI Il In', Il I Ill I! ....n,

Patented Dec. 26, 1939 UNITED STATES PATENT OFFICE METHOD OF DRYING VULCANIZED FIBER SHEETS Application June 27, 1938, Serial No. 216,187

9 Claims.

This invention relates to a method of drying sheets of laminated vulcanized fiber which produces a at sheet without cracks and delaminations. In the manufacture of such sheets an absorbent paper web is saturated with a cellulose peptizing (vulcanizing or parchmentizing) Y solution such as zinc chloride, sulphuric acid, phosphoric acid, calcium thiocyanate, cuprammonium. hydroxide and the like. The saturated web is then laminated, usually by winding the same upon a drum or cylinder until the desired sheet thickness is attained, and the resultant tube is split and attened to form the sheet. The action of the peptizing (vulcanizing or parchmentizing) agent having proceeded to the desired extent, the sheet is pured, i. e., it is submitted to soaking in baths of dilute solutions of the peptizing agent and of water to remove the peptizing agent, fol- 20 lowing which it is dried.

In the usual drying operation the sheet is simply placed in a drying house and allowed to remain until the contained water has been eliminated. The elimination of the heavy Water content of the sheet is accompanied by development of heavy internal stresses resulting from the fact that a declining moisture gradient is developed from the center to the outer surfaces of the sheet and shrinkage of the sheet is substantially proportional to the amount of water eliminated. The uneven distribution of the forces thus generated causes buckling of the body of the sheet and cracking and delamination of the marginal portions thereof with attendant losses of considerable magnitude.

In accordance with my invention, instead of delivering the sheet directly to the drying house after puring, I subject the same to a preliminary drying, during which the outer surfaces of the 40 sheet are kept moist vuntil the interior of the 'sheet is dried suiliciently to enable thev same to be safely subjected to a more rigorous drying operation, at which time the completion of the drying of the sheet will be substantially uniform and cracking, warping, bowing and delamination will be eliminated. The invention is particularly applicable in the treatment of relatively thick sheets such as may be formed when zinc chloride is used as the peptizing solution.

be applied in amounts approximately proportional to the tendency of' the sheet to dry at different points; that is to say, where the sheet is drying fastest the greatest amount of 'moisture 55 will be applied, and vice versa.

In moistening the sheet, the moisture should Obviously, the portion of the sheet which dries most rapidly is the marginal portion thereof, and I have found that the moisture can be most conveniently applied by utilizing an arrangement such as illustrated in the attached drawing in 5 which Fig. 1 is a face elevation of a sheet undergoing treatment in accordance with my invention; and

Fig. 2 is an edge elevation thereof.

In these gures the numeral I designates the l0 laminated vulcanized sheet and Il a strip of felt or other absorbent material such as pulp, or the like. This strip, as illustrated, is placed around the edges of the sheet, lapping over the edges thereof a suitable distance, for example from l three to ten inches, and is kept in a moistened condition. While plainv water may be employed, it is preferable to employ a water solution including a material reducing the vapor pressure of the water, such as sodium chloride, or any other salt. Most advantageously,l a hygroscopic agent is included in the solution such as glycerin, glycol, diethylene glycol and invert sugar and similar materials, the solutions being concentrations of between l0 and 50 per cent.

The sheets are kept in a horizontal position, with the cylinder or concave side of the sheet turned downward, at ordinary room temperatures, or at a low temperature for an extended period, depending upon the thickness of the laminated sheet material, with the strips thus applied, the strips being soaked with the solution either by continuously dripping the solution thereon or by moving the strips periodically and resoaking the same. If the strips are removed, the exposed faces of the sheet may be moistened with the water solution. In the case of relatively thick sheets,for example, sheets of two inchesv thickness, anperiod of eight days of treatment is usually recommended. At the close of the period 40 of treatment, the strips are removed and the fiber sheet placed in the dry house and dried in the usual fashion, at which time there will be no warping, splitting or cracking of the sheet.

The same result may be obtained by applying paraiiine to the edges of the sheet, thus preventing the evaporation of moisture from these portions thereof. With the application of paranne, y moistening of the edges of the sheet or of the material applied thereto becomes unnecessary, otherwise the treatment of the sheet remains the same as that previously described.

Since the method described is, obviously, capable of considerable variation without departing from the spirit of my invention, I do not wish to be understood as limiting myself thereto except as hereinafter claimed.

I claim:

1. 'Ihe method of preventing cracking and delamination of laminated vulcanized ber sheets during drying thereof comprising preliminarily drying the interior of the sheet while concentrating an aqueous moistening agent at the side edges thereof.

\2. The method of preventing cracking and delamination of laminated vulcanized ber sheets during drying thereof comprising preliminarily drying the interior of the sheet while concentrating an aqueous moistening agent at the side edges thereof and periodically moistening the exposed surfaces of the sheet.

3. The method of preventing cracking and delamination of laminated vulcanized ber sheets during drying thereof comprising preliminarily drying the interior of the sheet while concentrating an aqueous solution of a material lowering the vapor pressure of the water at the side edgesl of the sheet.

4. The method of preventing cracking and delamination of laminated vulcanized ber sheets during drying thereof comprising preliminarily drying the interior of the sheet while concentrating an aqueous solution of a material lowering the vapor pressure of the Water at the side edges of the sheet and periodically moistening the exposed surfaces of thesheet with said solution. v

5. 'Ihe method of preventing cracking. and delamination of laminated vulcanized ber sheets during drying thereof comprising preliminarily drying the interior of the sheet while concentrating an aqueous solution of a hygroscopic agent at the side edges of the sheet.

6. The method of preventing cracking and delamination of laminated vulcanized ber sheets during drying thereof comprising preliminarily drying the interior of the sheet While concentrat ing an aqueous solution of a hygroscopic agent at the side edges of the sheet and periodically moistening'the exposed surfaces of the sheetv with said solution.

7. The method of preventing cracking and delamination of laminated vulcanized ber sheets during drying thereof comprising preliminarily drying the interior of the sheet While concentrating an aqueous solution of a hygroscopic agent the edges of the sheet and equalizing the drying process in the exposed surfaces thereof.

9. The method of claim 8 wherein a felt is applied to the edges of the sheet and kept in a moistened condition during preliminary drying operations;

NORMAN G. JONES. 

